There has been a history of over 30 years in research on bioactive glass since 1971 when Dr. Larry Hench reported that such glass could bond together with bone tissues for the first time. Also, such glass material has been used for restoration of bone defects in clinical practice for over ten years, and such clinical applications have proven successful in that this glass can bring along not only the benefit of osteoconduction, but also the bioactivity to stimulate the growth of bone tissues. Many recent studies have revealed that the degradation products of bioactive glass can enhance the generation of growth factors, facilitate cellular proliferation and activate gene expression of osteoblasts. Moreover, bioactive glass is the only synthetic biomaterial so far that can both bond with bone tissues and soft tissues. These unique features of this glass have created a great potential for its clinical application as a type of medical device, and thereby, attracted great attention from both academia and the industrial sector. Despite its excellent biocompatibility and bioactivity, bioactive glass can be now produced only in a granular form for clinical application. For restoration of bone defects, macroporous and block scaffold materials with a particular mechanical strength are often needed to fill in and restore such defects. Even in the field of tissue engineering, which receives world-wide attention and evolves rapidly, macroporous bioactive scaffold materials are similarly demanded to serve as cell carriers.
Research studies in the past have suggested that besides the composition of the material, its structure can directly influence its clinical applications as well. The macroporous and block scaffold materials with bioactivity whose pore sizes are in the range of 50-500 microns are most suitable to be used as materials either for the restoration of bone defects, or as cell scaffolds. Any macroporous biomaterial having a pore size within the said range can bring benefits to the housing and migration of cells or tissue in-growth, as well as to the bonding of such a material to living tissues, thereby achieving the goals of repairing defects in human tissues and reconstructing such tissues more effectively.
Moreover, the subject of the biomaterials that are both resorbable and macroporous has now become an integral part of tissue engineering studies that have been rapidly developed in recent years, where scaffolds made of such macroporous materials can be adopted to serve as cell carriers so that cells can grow in the matrix materials and constitute the living tissues that contain genetic information of the cell bodies, and such tissues can be in turn, implanted into human bodies to restore tissues and organs with defects. Therefore, resorbable, macroporous bioactive glass scaffold materials possess wide-ranging potential for their applications as cell scaffolds either for restoration of defects in hard tissues, or for the purpose of in vitro culture of bone tissues.
U.S. Pat. Nos. 5,676,720 and 5,811,302 to Ducheyne, et al, teach a hot-pressing approach using inorganic salts such as calcium carbonate and sodium bicarbonate as the pore-forming agents to prepare and manufacture macroporous bioactive glass scaffolds which have the compositions of CaO—SiO2—Na2O—P2O5, and which are designed to function as the cell scaffolds used for in vitro culture of bone tissues. Nevertheless, this hot-pressing approach if adopted would entail high production costs, and furthermore, controlling the composition of the finished products is difficult because the composition will be affected by the remnants that result after sintering the inorganic salts used as pore-forming agents. Additionally, Yuan, et al. have adopted oxydol as a foaming agent to prepare and manufacture 45S5 bioactive glass scaffolds under a temperature of 1000° C., with the scaffolds produced in this way being bioactivity and having the ability to bond together with bone tissues (J. Biomed. Mater. Res; 58:270-267, 2001). But according to our testing results, the glasses will become substantially crystallized and their resorbability/degradability will decrease if they are sintered under a temperature of 1000° C. In addition, it is quite difficult to control the pore size and pore number of the materials when oxydol is used as the foaming agent.
Mechanical strength is also an important factor for performance of macroporous bioactive glass scaffold materials, and relevant studies have suggested that any compressive strength below 1 MPa would result in the poor applicability of these scaffold materials, and thus, in the course of applying them either as cell scaffolds or for the purpose of restoration of bone injuries, such materials would be very prone to breakage or damage, therefore limiting the effectiveness of their application. So far, no report on the compressive strength standard data of macroporous bioactive glass scaffolds has been found in previous patent and published documents and as a result, gives rise to the purpose of this invention to determine proper technical control measures to keep the compressive strength of the manufactured bioactive glass scaffold within a certain range to meet the requirements of various applications.